The present invention is directed generally to infusion systems, and more particularly to an implantable microinfusion pump system for dispensing a fluid medicament at a prescribed rate within the human body over an extended period of time.
Implanted microinfusion pump systems are advantageously employed where a medicament is to be dispensed to an ambulatory patient on a regular basis over an extended period of time, as where insulin is dispensed in the treatment of diabetes, or where chemotherapeutic drugs are dispensed in the treatment of cancer. In performing these and other internal body procedures such pump systems must be reliable in operation, must be sealed against body fluids, must hold a sufficient quantity of medication so as to avoid the need for frequent refills, and must be refillable when nearly empty to preclude interruption of the medication schedule. Furthermore, such pump systems must be physically small so as to be readily implantable without unnecessary disturbance to the body, and must be operable on their own internal batteries for a sustained period of time.
One drawback of previous implantable microinfusion pump systems has been the relatively short life of the pump batteries because of the extended current demand of the pump actuator circuitry while dispensing the relatively slow moving medicament. The microinfusion system of the present invention overcomes this drawback by limiting current demand to a refill stroke of short duration, the pump stroke being accomplished by a permanent magnet at a rate compatible with the desired medication delivery rate.
Another drawback of previous implantable pumps has been the undesirably large size and complexity of the pump housings. The pump system of the present invention utilizes a compact hermetically sealed housing wherein the pump mechanism is positioned within a pump body member which extends between opposite parallel-spaced walls of the housing. The batteries and circuitry for actuating the pump are contained within the housing, which is formed to provide in conjunction with an adjacent flexible wall a reservoir for medicament to be infused.
Still another drawback of previous microinfusion pumps has been that their valving arrangements were undesirably subject to wear with extended use, and did not prevent uncontrolled flow of medicament when the pump apparatus was subjected to high external pressures. The present invention provides a valve arrangement which minimizes friction between the pump piston and valve surfaces, thereby minimizing wear, and which provides positive protection against uncontrolled flow of medicament in the event of externally applied pressures.